Comparative evaluation of physicochemical qualities of flours from steam-processed yam tubers

Three factors were comparatively evaluated during the atmospheric steaming of yam tubers and down-stream processing of the resultant flours. White yam (Dioscorea rotundata Poir), water yam (D. alata L.) and yellow yam (D. cayenensis Lam) tubers were used for this investigation. The effects of yam tuber variety (white, water and yellow), tuber steaming time (30, 60, 90, 120 min) and flour particle size (75, 125, 150, 180, 250, 375, 500 μm) on the physicochemical quality of yam flour were studied. The magnitude and extent of the factorial influence were measured/conducted using the effects on water absorption capacity, swelling index, iodine affinity of starch, solubility and gelatinization temperature. All three variables were observed to cause significant differences (P⩽0.05) in all the test parameters of flour. Based on the results, it is recommended that (from an economic standpoint) tubers of water/yellow yam be steamed at a minimal time of 60 min and pulverized into flours of particle sizes of not less than 75 μm and not more than 375 μm. This combination will give rise to a steamed yam flour sample which exhibits optimum physicochemical characteristics.